1. Field of the Invention
The invention is related to microprocessors and microprocessor technology, and in particular to microprocessor timers.
2. Background Information
Microprocessors use clocks to synchronize the operations of the various circuits inside the microprocessor. The bus speed and a clock multiplier determine the speed at which the microprocessor core runs. For example, an Intel(copyright) Pentium(copyright) II 266 megahertz (MHz) microprocessor typically has a bus speed of 66 MHz and a clock multiplier of four.
From time to time computer users may try to run their microprocessors at higher speeds, ostensibly to get better performance. This typically is referred to as xe2x80x9cover clocking.xe2x80x9d There are many risks associated with over clocking, however. For example, operating at frequencies greater than the designed frequency can cause the microprocessor to overheat, which can cause it to become unstable, experience data corruption errors, etc. Over clocking can void warranties, shorten the microprocessor""s lifespan or the lifespan of other computer components. Sometimes, an over clocked microprocessor cannot be returned to its normal frequency and the effects of over clocking remain forever. This means that the microprocessor may be permanently damaged.
To minimize over clocking, conventionally, the microprocessor has an integrated reference timer that monitors the frequency. If the timer detects that the microprocessor is running too fast, the timer will initiate a microprocessor shut down.
Conventional reference timers are capacitor-based, which have limitations, however. The behaviors of the on-die capacitors used are difficult to predict, primarily due to variation in capacitor manufacturing processes. Integrated capacitors tend to be non-linear, as well. The non-linearity and process sensitivity reduce the viable range over which a capacitor""s voltage can be charged. Sometimes the variations are so extreme that it is difficult to accurately determine frequencies and the timer fails to initiate a microprocessor shut down in response to over clocking.
The first solution is to use a single capacitor and ramp it up and down multiple times. This solution is troublesome because errors accumulate for each ramp up transition and each ramp down transition. The accumulated errors result in a loss of precision that may be intolerable.